Eastern equine encephalitis is a very rare viral disease that primarily affects horses but can be transmitted to humans through the bite of infected mosquitos. It is not very virulent and in general only one out of every 25 people infected will actually develop symptoms. However, infected individuals suffer a very high rate of brain damage, even though deaths are very uncommon.
The disease remains rare as most horses are vaccinated against the condition. It is also very geographically limited, affecting primarily people living on the east coast of the United States. There are an average of ten human cases a year. Vaccination is recommended for people who live where the disease is endemic. Mosquito control is also used to prevent the spread of the disease.